The skin of organisms such as humans serves as a protective barrier that, among other functions, prevents pathogens from entering the body and prevents or regulates fluids such as blood and water from exiting the body. In the field of modern medicine, there is often a need to deliver injectates such as drugs through the skin and into the bloodstream of patients. Traditionally, this delivery of liquids into a patient's body is accomplished by insertion of a needle through the patient's skin and into an area inside of the patient's body where the liquid can enter the patient's blood stream.
However, the use of needles to deliver liquids into a patient's body has a number of significant drawbacks such as the pain associated with being pierced by a needle, the fear that many patients have of needles, and the skin damage and associated risk of infection that occurs due to the use of needles.
As a result, needle-free transdermal injection devices have been developed. These devices use a high pressure, narrow jet of injection liquid or powder to penetrate a patient's skin, obviating the need to pierce the patient's skin with a needle.
One way to deliver a drug is to place it inside a cylinder having a piston at one end thereof, and to drive the piston impulsively to provide the necessary pressure to separate the skin cells. Unfortunately, pressure acts in all directions, and in particular, acts against the wall of the cartridge. This causes the wall to bow outward and/or compress, thus increasing the volume of the cartridge and reducing the overall pressure. This deformation is more likely to occur during periods of rapid acceleration which can lead to imprecise delivery (i.e., incorrect dosage) and even malfunction. The lost injection energy and decrease in acceleration of the injectates can also “wetness” (i.e., residual injectate on the skin).
Increasing the thickness of the wall does not prevent deformation of the inner wall of the cartridge (e.g., bending, buckling, or compression). Even relatively thick glass or medical grade plastic cartridges can compress under certain delivery pressures as those materials are not sufficiently rigid.